Using the Uniqueness Plug-In With Replication

The UID uniqueness plug-in does not perform any checking on attribute
values when an update is performed as part of a replication operation. This
does not affect single-master replication, but the plug-in cannot automatically
enforce attribute uniqueness for multimaster replication.

Single-Master Replication Scenario

Because all modifications by client applications are performed on the
master replica, the UID uniqueness plug-in should be enabled on the master
server. The plug-in should be configured to enforce uniqueness in the replicated
suffix. Because the master ensures that the values of the desired attribute
are unique, you do not need to enable the plug-in on the consumer server.

Enabling the UID uniqueness plug-in on the consumer of a single master
does not interfere with replication or normal server operations. However,
it might cause slight performance degradation.

Multimaster Replication Scenario

The UID uniqueness plug-in was not designed for use in a multimaster
replication scenario. Because multimaster replication uses a loosely consistent
replication model, simultaneously adding the same attribute value on both
servers will not be detected, even if the plug-in is enabled on both servers.

However, you can use the UID uniqueness plug-in if the attribute on
which you are performing the uniqueness check is a naming attribute, and the
uniqueness plug-in is enabled for the same attribute in the same subtrees
on all masters.

When these conditions are met, uniqueness conflicts are reported as
naming conflicts at replication time. Naming conflicts must be resolved manually.
For more information, refer to Solving Common Replication Conflicts.